Acid cleaning composition



Patented June 21, 1949 WW F53 Con/W UNITED STATES PATENT OFFICE ACID CLEANING COIWPOSITION Francis N. Alquist and Charles W. Hopkins, Midland, Mich., assignors to 1he Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Application May 2, 1947, Serial No. 745,634

3 Claims.

1 The invention relates to methods of removin acid-soluble deposits from ferrous metal surfaces. It more particularly concerns an improved acid composition effective for dissolving oxidic scale 2 tion brings about the solution of iron metal in accordance with the equation:

from ferrou metal urfaces 5 wherein 2Fe represents 2 55.84 grams of meal Hydrochloric acid solutions are oftentimes used lie iren dissolved or each 5 grams of fe c for cleaning ferrous metal surfaces of deposits iron in the foreign material dissolved from the comprising acid-soluble material. The materials surface of the metal by the dmost readily removed from ferrous metal by hy- Our observations have shown that the reducing drochloric acid are those containing 0r composed a n f h m tal being clean d p s inof a carbonate, such as a calcium carbonate, the dependently 0f e a t by e ac d however 3 iron oxides, such as ferrous oxide, ferric oxide well inhibited by the usual inhibitors and that 1 and ferrosoferric oxide; although other deposits the usual inhibitors do not substantially inhibit 1 including silicates and phosphates are sometimes the foregoing redu action of e m tal- As sufliciently soluble and to be removed by the disa consequence, the removal from a ferrous metal solving action of t i I employing hysurface of ferric iron containing foreign matedrochloric acid solution for cleaning ferrous rial y disseivihg the same n inhibited ydrometal, it is the usual practice to incl d i th chloric acid results in dissolving metallic iron acid an acid-corrosion inhibitor which reduces or from the f ro metal b n n d in an prevents the metal from being attacked by the amount Which p s p n the mount of feracid without interfering with the action of the tie iron compound dissolved by he a dacid on the materials to be removed from the e amount of iron metal d ed y the acid meta], Common inhibiting agents employed for itself (as distinguished from that dissolved by the purpose are organic sulphur compounds, such reduction as explained above), while the acid is as mercaptans, organic nitrogen bases, such as attacking the acid-soluble materials on the surand quinoline or crude products conface of the metal, may be computed from the taining tli'fii'iiibliasdoal tar bases, and certain following eq at metallic compounds, such as thesoluble arsenic compounds. I Fe+2HC1 FeC12+H2 While the rate of corrosion of the metal due the amount of hydrogen evolved being taken as to attack by the acid solution during cleaning a measure of the amount of acid-corrosion or is usually greatly lessened by the use of convenattack by the acid on the ferrous metal being tional acid-corrosion inhibitors, we have found ean d. that when the materials being removed from the The conventional acid cleaning compositions metal comprise ferric or ferrosoferric compounds for removing by dissolution e foreign matter. the rate of corrosion of the metal in the cleaning u h as scale and the like which becomes desolution is increased, in spite of the presence of posited p n f rous etal surfaces in various even the most effective acid-corrosion inhibitors y leave much t be desired as t e p known. We have found, for example, that either sitions, however well inhibited against acid-corferric oxide or ferrosoferric oxide, added to the 40 resien, become y o r s ve to fer ous metal conventionally inhibited hydrochloric acid solusurfaces particularly h e of iron and steel when tion, increases its corrosiveness to the metal. applied to deposits thereon that p e a e ric Similar observations have been made of increased compoundcorrosion of scaled boiler metal and the like, It is an Object Of the P nt invention o p carrying ferri ir compounds i t m vide an improved hydrochloric acid aqueous solupared to i l Scaled metal carrying either less tion suitable for dissolving from a, ferrous metal or no ferric iron compounds The explanation surface material comprising a ferric iron comfor the increased corrosion attributable to the pound w1th a reduced amount of cPrmsionpresence of ferric iron compounds in the mateother 9 3 and aiivantaiges W111 appear as rlal being removed from the metal by the conthgfieicnptlqn the tnventlon proceed? e invention is predicated upon the discovery ventionally inhibited acid solution is that metalthat by including glyoxal in conventionally he iron of the metal bemg cleaned reduces the hibited aqueous solutions containing hydrochloric ferric iron compounds to ferrous s they become acid ferrous metal surfaces may be cleaned theredissolved by the acid solution and such reducwith of ferric iron containing deposits with re- 3 duced attack on the metal compared to the amount of attack obtained when the inhibited acid solution is used without the addition of the aforesaid glyoxal.

The invention, then, consists in the ferrous metal cleaning composition and method of cleaning ferrous metal therewith, hereinafter more fully described and particularly pointed out in the claims. 7

In carrying out the invention, aqueous hydrochloric acid solution is used in a concentration suitable for decomposing, dissolving, or disintegrating the materials to be removed in cleaning the ferrous metal surface. Complete solution of the materials to be removed from the metal surface is not always necessary as some deposits contain both acid-soluble and acidinsoluble constituents and such deposits usually slough off when attacked by the acid without completely dissolving. The concentration of the acid is chosen with due regard for the ease with which the solution will attack or disintegrate the materials to be removed. A concentration between about and 25 per cent of E01 by weight is usually suitable, although other concentrations can be used. A preferred concentration is about per cent of HCl. The more concentrated the acid the more difficult it becomes to inhibit its tendency to corrode the metal being cleaned, hence the lowest of the concentrations that will effectively clean the metal preferably is used.

To minimize the attack of the acid on the metal being cleaned a suitable inhibitor of acid-corrosion is added to the acid, as known in the art. A very large number of substances and products are known that have the --property of inhibiting the acid-corrosion of iron or steel. Examples of these materials have been mentioned already. Generally, the amount used is in the range of 0.1 to 2 per cent by weight or volume of the acid solution,'although other proportions may be used according to the effectiveness of the material for the purpose and the degree of suppression of acid-corrosion it is desired to produce.

In order to suppress the corrosion of the metal resulting from its reduction of the ferric compounds in the materials being cleaned from the metal to ferrous compounds in accordance with the first equation above, we add to the acid solution, in addition to the acid-corrosion inhibitor, a quantity of glyoxal. The glyoxal has the property, when used in combination with an acid-corrosion inhibitor as herein described, of reducing the amount of corrosion which otherwise occurs of the metal being cleaned as a result of the normal tendency of the metal to reduce the ferric compounds diyssolved from the deposits to ferrous compounds. The glyoxal so used becomes oxidized or consumed instead of the metal being cleaned, thus educing the total amount of corrosion of metal. The amount of glyoxal to be used is preferably in excess of that approximately stoichiometrically equivalent to the ferric iron content of the material to be removed from the surface of the metal and may be several times as much. The stoichiometrical proportion of glyoxal to ferric iron is approximately 0.5 gram molecular weight for each gram molecular weight of ferric iron. Concentrations in the acid solution of from 0.3 to 5 per cent have been used effectively, although other amounts may be used.

To ascertain the amount of ferric iron which may be present in the material to be removed from the metal, one may resort to a conventional analysis of the material and a measurement of the approximate amount of the material per unit area of the surface to be cleaned. From this data and knowledge of the area of the ferrous metal surface to be cleaned the total weight of the ferric iron material that is to be dissolved by the acid solution may be computed. The amount of glyoxal to be employed may be ascertained as aforesaid by using somewhat more than one-half of a gram molecular weight of glyoxal for each gram molecular weight of ferric iron thus computed to be present.

The amount of acid-soluble material to be removed, in addition to the ferric iron content thereof, may be used to determine the quantity of acid which will be consumed, but the amount to employ is normally far in excess of that consumed in a cleaning operation. In removing the foreign material from the internal surface of a vessel having a large volume, for example, as by filling the vessel with the. acid solution, a very much larger quantity of acid is necessarily employed than will be needed for actually dissolving and disintegrating the materials to be removed from the metal surface. This is usually the case in treating the internal surfaces of steam generating equipment, such as steam boilers, as the interior of the vessel must be filled completely with th acid solution to reach every part and the concentration of the ingredients in the acid solution must necessarily be high enough to produce reasonably rapid action. The total amount of active ingredients of the cleaning solution is, therefore, as a rule in excess of the amount to be consumed.

Example The following example is illustrative of the practice of the invention and comprises the cleaning of the internal surfaces of a conventional steam generator having an internal volume of 15,500 gallons. The composition of the foreign material forming the deposit to be removed from the interior surfaces of the generator was approximately one-third ferrosoferric oxide, the balance being essentially calcium hydroxy phosphate and hydrated magnesium silicate. The generator was filled with a hydrochloric acid solution containing 7.3 per cent of HCl by weight, 62 gallons of an acid-corrosion inhibitor solution comprising by volume approximately one-third of concentrated sulphuric acid (98 per cent), one-third of crude quinoline, and one-third of water, and 49 gallons of an aqueous solution containing 32.8 per cent by weight of glyoxal. The foregoing materials were introduced into the generator in a period of about 82 minutes and allowed to remain in it for about 8 hours at which time samples of the spent acid indicated that the cleaning action was substantially complete, During the acid treatment, hydrogen was evolved and vented from the system. The temperature during the treatment was maintained in the range of about to F. Thereafter, the spent acid was drained from the generator. The drained generator was rinsed with water and then filled with a 1 per cent aqueous solution of sodium carbonate and the solution boiled in the generator for 1 hour to remove traces of acid and any absorbed hydrogen from the metal. Following this operation, the generator was drained and examined. The examination of the surfaces showed them to be free from foreign deposits and the metal smooth and free from signs of corrosion attack by the cleanin solution. The acid after spending had declined to EXAMINESD a concentration of 6.07 per cent HCl and contained 1.28 per cent of iron all in the ferrous state. Approximately 86 pounds of the glyoxal was oxidized, indicating a saving of generator metal of approximately 248 pounds beyond that saved from acid-corrosion.

Another advantageous action of the inhibited hydrochloric acid solution containing glyoxal, in its use in descaling ferrous metal, is that the metal is not pitted by corrosion which normally occurs when conventionally inhibited hydrochloric acid solutions are used without glyoxal,

As illustrative of the effect on the corrosion rate of iron and steel of the addition of glyoxal to conventionally inhibited hydrochloric acid solution, the following data are cited: It is found that the corrosion rate of mild steel test pieces in per cent of hydrochloric acid solution containing 0.4 per cent of crude quinoline. as an acidcorrosion inhibitor, was 0.044 poun per square foo per ay a 75 F. Similar pieces of mild steel subjected to the action of the same hydrochloric acid solution to which was added 1.6 per cent of ferrosoferric oxide corroded the metal at the rate of 0.077 pound per square foot per day. When 0.801 per cent of glyoxal was added to the latter solution and the rate of corrosion of mild steel was determined, it was found to be 0.044 pound per square foot per day. In other words, the corrosiveness of the conventionally inhibited acid solution was greatly increased in the presence of ferric iron but reduced to the same corrosiveness, by the addition of glyoxal, as conventionally inhibited hydrochloric acid in the absence of ferric iron. Similar results have been obtained with other acid-corrosion inhibitors and other proportions of ferrosoferric oxide and glyoxal in comparing the effect, on corrosion rate of mild steel in inhibited hydrochloric acid solution, of the addition of glyoxal to the inhibited acid solution both with and without the addition of ferrosoferric oxide. In every case, the addition of the ferrosoferric oxide, in the absence of glyoxal, greatly increased the corrosion rate of mild steel in conventionally inhibited acid while the addition of glyoxal reduced the corrosiveness of the inhibited acid solution in the presence of ferrosoferric oxide.

For the purpose of computing the amount of metallic iron saved from corrosion, the evolution of hydrogen, when the acid solution is employed in removing a foreign material from ferrous metal, is taken as a measure of the amount of attack by the acid on the ferrous matter in accordance with the second equation above; and the decrease in the weight of the metal being treated, exclusive of the foreign material there'- with, is taken as the amount of corrosion of the metal produced both by acid corrosion and corrosion due to reduction of ferric compounds. With the foregoing in view, the following example is illustrative of the amount of metallic iron saved from corrosion according to the first equation above, due to the addition of glyoxal to the acid solution. In this example, the acid contained 10 per cent of HCl and 0.4 per cent of crude quinoline as an acid-corrosion inhibitor. Test pieces of mild steel strips were immersed therein at 175 F. for 2 hours during which the evolved hydrogen was collected. When no glyoxal was present 54.5 cc. of hydrogen were evolved per test piece indicating that 0.142 gram of metal was dissolved by the acid. But the actual average loss in weight of iron of the steel pieces was 0.362 gram. Therefore, 0.220 gram more iron was dissolved altogether than that dissolved by the acid alone, and, since the acid solution was found to be free from dissolved ferrosoferric iron, the difference between the total weight of iron dissolved and that corresponding to the acid corrosion is, therefore, the amount of iron metal dissolved in reducing the ferric iron to ferrous. When exactly similar tests were made but with the addition to the inhibited acid solution of 0.80 per cent of a glyoxal, the actual average weight loss of the metallic pieces was only 0.263 gram. According to the hydrogen evolved, which was 63.5 cc., 0.185 gram of the iron weight loss was due to acid attack. Hence the difference between the total metal dissolved. i. e. 0.263 gram, and the amount of metal dissolved by the acid, i. e. 0.158 gram, is the amount of corrosion due to reduction of ferric iron by the metal, viz., 0.105 gram. Thus, the amount of ferric iron corrosion in the absence of glyoxal was approximately 60.8 per cent of the total corrosion while in the presence of glyoxal, the amount of ferric iron corrosion was only per cent of the total.

Thus, desirable savings in the amount of metal dissolved due to its reducing action on ferric compounds in the materials to be removed from the metal are obtained, when glyoxal is present in the acid cleaning solution together with a conventional acid-corrision inhibitor.

We claim:

1. A composition for cleaning a ferrous metal surface comprising an aqueous solution containing from 5 to 25 per cent of HCl, from 0.1 to 2 per 40 cent of an organic nitrogen base selected from the group consisting of pyridine and quinoline and from 0.1 to 5 per ceniiglyox l.

2. A composition for c eaning a ferrous metal surface comprising an aqueous solution containing from about 5 to 25 per cent of HCl, from 0.1 to 2 per cent of quinoline, and from 0.1 to 5 per cent of glyoxal.

3. A composition for cleaning a ferrous metal surface comprising an aqueous solution containing from about 5 to 25 per cent of HCl, from 0.1 to 2 per cent of pyridine, and from 0.1 to 5 per cent of glyoxal.

FRANCIS N. ALQUIST. CHARLES W. HOPmNS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,678,775 Gravell July 31, 1928 1,773,247 Williams Aug. 19, 1930 1,961,096 Cunningham May 29, 1934 2,010,562 Parkes Aug. 6, 1935, 2,072,003 Lutz Feb. 3, 1937 2,172,147 Vaughen Aug. 16, 1938 2,384,467 Hill Sept. 11, 1945 

